Remotely controlled and/or autonomously controlled aircraft, generally referred to as drones, are used in a wide range of applications. For example, drones are commonly used for surveillance purposes. In such examples, the drones may be expected to remain in flight for long periods of time.
In general, drone aircraft are either helicopter-type aircraft that take off and land vertically, or fixed-wing aircraft that require an extended open space (e.g., tens or hundreds of meters) for takeoff and landing. The helicopter-type aircraft, also referred to as “quadcopters” or “multicopters,” require substantial energy expenditure to hover and remain aloft, and thus generally cannot perform flights of more than thirty to fifty minutes. In particular, the flight time is limited in battery-powered multicopter aircraft because of the low energy density of modern electrical energy storage technologies such as lithium-ion batteries. Multicopters further have low maximum flight speeds which, combined with short flight times, severely restrict the geographical area over which they can perform surveillance.
In contrast, fixed-wing aircraft can remain aloft for extended periods of time with relatively lower energy expenditure. However, as noted above, they require an extended open space for takeoff and landing.
Specialized fixed-wing aircraft that do not need a large footprint to take off have been developed. However, such aircraft require the use of a ground-based propulsion system to take off (e.g., a linear catapult), require separate power systems for hovering and flying (a plane/helicopter hybrid), or require power systems that change orientation (for example, a tiltrotor). These approaches suffer from several disadvantages stemming from complicated mechanical systems and/or excess weight. The complicated mechanical systems increase maintenance costs as there are more parts to break. The greater weight forces the designer to increase the overall size of the aircraft or the minimum speed at which the aircraft has to operate to avoid stalling. The increase in weight also increases parasitic drag upon the aircraft, and thereby increases the energy required to carry out flight missions and cuts back on flight time. These disadvantages are further magnified in aircraft using an electric power train due to the low energy density available in electrical energy storage technologies.
A need therefore exists for a fixed-wing aircraft capable of remaining aloft for an extended period of time, and capable of vertical takeoff and landing. Such an aircraft could advantageously be used, for example, but not limited to, for surveillance purposes or the delivery of items in locations where there is no room for a sufficient airstrip (e.g., protected wilderness, national parks, dense cities).